These studies are designed to provide quantitative data on the effects of exposure of the prenatal rat to ultrasonic energy. Exposures are being made to graded time-intensities of ultrasound at representative times of gestation under conditions which simulate pulse-echo, Doppler, and diathermy techniques. Detailed characterization of the ultrasonic beams are made, as well as estimates of the energy absorbed by the conceptus. Measurements of temperature elevation during exposure are being analyzed and attempts to detect cavitation and resonance are in progress and models are being developed. In some experiments, the exposed animals are sacrificed at 20 days of gestation, prenatal mortality noted, and the fetuses examined for the presence of malformation. In other experiments, the animals are allowed to deliver and the incidences of mortality and gross anomalies of the offspring are studied, with particular emphasis on neurological, behavioral, or reproductive deficits or, in some cases, on the cardiovascular system. The incident and absorbed energies associated with varous clinical procedures will be estimated. These values will be compared with the "dose-effect" relationships and threshold estimates obtained from these experiments. These will allow an analysis of the safety and/or hazard associated with current clinical techniques.